A known master cylinder includes a cylinder body, a reservoir, and a reservoir fluid passage that is equipped with a valve mechanism and that is arranged between a pressure chamber provided at the cylinder body and the reservoir. The reservoir fluid passage has a high suction performance, i.e., performance for supplying a brake fluid from the reservoir through the pressure chamber in response to a request for a supply of the brake fluid from a hydraulic control system that is electronically controlled. The valve mechanism is provided for preventing the brake fluid from suddenly counterflowing from the pressure chamber disposed at the cylinder body to a fluid chamber disposed at the reservoir. Such master cylinder is disclosed in JP2693154B. According to a structure of a master cylinder in which a leg portion provided at a reservoir tank (hereinafter simply referred to as a “reservoir”) is positioned within a reservoir connection port formed at a cylinder body, and a valve mechanism (valve apparatus) is arranged at a lower side of the leg portion, a bottom surface of the reservoir is positioned relatively high and thus a performance for accornmodating the master cylinder within an engine room deteriorates. Thus, the master cylinder disclosed in JP2693154B includes a receiving portion formed inside (precisely, at a bottom portion) of the reservoir so as to receive a valve body of the valve mechanism at a position higher than the bottom surface. Accordingly, the bottom surface of the reservoir is prevented from being positioned relatively high. Further, the master cylinder includes a supply passage for the brake fluid formed at a sidewall of the receiving portion to thereby consume the brake fluid up to the bottom surface within the reservoir.
According to the master cylinder disclosed in JP2693154B, a relief pressure generated by the valve mechanism is received by the reservoir. Therefore, the relief pressure causes the reservoir to be upwardly pushed, which may lead to a lifting of the reservoir, a disengagement of the reservoir from the cylinder body, a breakage of the reservoir, and the like. In addition, a slit and a lateral bore are formed at the reservoir for supplying the brake fluid from the reservoir by bypassing the valve mechanism and for returning the brake fluid to the reservoir after the brake fluid passes through the valve mechanism, respectively, while the receiving portion (precisely, a wall thereof) is formed to be higher than the bottom surface of the reservoir. As a result, a molding performance of the reservoir may be difficult.
A further downsizing of the master cylinder is necessary while a mounting space thereof is limited within the engine room. On the other hand, the elimination of concerns about the disengagement of the reservoir from the cylinder body and the breakage of the reservoir, the improvement of the molding performance of the reservoir, and the like are also required.
A need thus exists for a master cylinder which is not susceptible to the drawback mentioned above.